Water Heaters: Types, Venting, and the First Install You Will Touch

45 min read Training Guide

Tank and tankless water heater types, gas and electric basics, venting options, and the T&P and expansion requirements on every install.

Table of contents

What the work looks like

Water heaters are the plumbing install a first-year apprentice is most likely to help with. Tank-type water heaters (gas or electric, typically 40 or 50 gallons residential) are the majority. Tankless (on-demand) water heaters are common in new construction and remodels. Hybrid heat-pump water heaters are growing fast due to rebates. Residential water heaters have an 8 to 15 year expected life; most replacements happen on emergency call when the tank leaks.

Safety and tools

Tank-type gas water heater components:

  • Cold water inlet (dip tube drops water to the bottom).
  • Hot water outlet.
  • Temperature and pressure relief valve (T&P, rated 150 psi / 210F) with a discharge tube terminating within 6 inches of the floor or to an approved drain.
  • Expansion tank on any closed system (where a check valve or backflow device prevents thermal expansion back into the main).
  • Drain valve at the base.
  • Anode rod (sacrificial magnesium or aluminum) that protects the tank from corrosion. Inspect every 3 to 5 years.
  • Gas valve, thermocouple, pilot or igniter, burner, and draft hood (for atmospheric vent) or inducer fan (for power vent).

Venting types:

  • Atmospheric (natural draft): metal B-vent through the roof. Requires combustion air from the room.
  • Power vent: inducer fan pushes combustion products out through sealed PVC or stainless flue to a sidewall termination. Sealed combustion air or ambient.
  • Direct vent (sealed combustion): concentric PVC draws combustion air in and exhausts products through a sidewall.
  • Electric water heaters: no vent required. Two 4,500W elements on a 30A 240V circuit typical.
  • Heat-pump water heater: pulls heat from ambient air and moves it into the tank. Needs ambient air volume and a condensate drain.

Every install requires:

  • Code-compliant shutoff valves on cold supply.
  • Dielectric union or brass nipples where copper meets steel.
  • T&P valve and discharge line sized per the manufacturer (typically 3/4 inch).
  • Expansion tank on any closed system.
  • Sediment trap (drip leg) on gas line.
  • Proper venting installed per manufacturer and NFPA 54.
  • Earthquake straps in seismic zones (California, Washington, Oregon, and others).

Tools: pipe wrenches, channel locks, tubing cutter, torch and solder (or press tool), T&P valve, dielectric connectors, expansion tank, and a hand truck rated for the weight (a full 50-gallon tank is 400+ pounds).

Safety: drain the tank before removing, shut the gas at the shutoff valve and cap or plug the line before disconnecting, and lockout the electrical breaker on electric units. Never light a pilot near a gas leak.

Your first exercise

Find a water heater in a house or building you know. Identify the vent type (B-vent going through the roof is atmospheric; PVC sidewall is power or direct vent). Check whether a T&P discharge line and expansion tank are present. That single walk-through covers 80 percent of what code inspectors look at.

Where to go next

Build on Water Heater Installation with Plumbing Fundamentals (Introduction to Plumbing), Pipe Fitting (PEX/Copper/PVC), Plumbing Code Basics (Introduction to Plumbing Code), Gas Line Installation Basics (Introduction to Gas Line Installation), Fixture Installation & Repair, Backflow Prevention (Introduction to Backflow Prevention). Safety: Workplace Safety, Fire Safety & Prevention, Hazardous Materials Handling.